SI4460-C2A-GM Datasheet, PDF (24/53 Pages) Silicon Laboratories – HIGH-PERFORMANCE, LOW-CURRENT TRANSCEIVER

Si4463/61/60-C
4. Modulation and Hardware Configuration Options
The Si446x supports different modulation options and can be used in various configurations to tailor the device to
any specific application or legacy system for drop in replacement. The modulation and configuration options are set
in API property, MODEM_MOD_TYPE. Refer to the API documentation for details on modem related properties.
4.1. Modulation Types
The Si446x supports five different modulation options: Gaussian frequency shift keying (GFSK), frequency-shift
keying (FSK), four-level GFSK (4GFSK), four-level FSK (4FSK), and on-off keying (OOK). Minimum shift keying
(MSK) can also be created by using GFSK with the appropriate modulation index (h = 0.5). GFSK is the
recommended modulation type as it provides the best performance and cleanest modulation spectrum. The
modulation type is set by the “MOD_TYPE[2:0]” field in the “MODEM_MOD_TYPE” API property. A
continuous-wave (CW) carrier may also be selected for RF evaluation purposes. The modulation source may also
be selected to be a pseudo-random source for evaluation purposes.
4.2. Hardware Configuration Options
There are different receive demodulator options to optimize the performance and mutually-exclusive options for
how the RX/TX data is transferred from the host MCU to the RF device.
4.2.1. Receive Demodulator Options
There are multiple demodulators integrated into the device to optimize the performance for different applications,
modulation formats, and packet structures. The calculator built into WDS will choose the optimal demodulator
based on the input criteria.
4.2.1.1. Synchronous Demodulator
The synchronous demodulator's internal frequency error estimator acquires the frequency error based on a
101010 preamble structure. The bit clock recovery circuit locks to the incoming data stream within four transactions
of a “10” or “01” bit stream. The synchronous demodulator gives optimal performance for 2- or 4-level (G)FSK
modulation that has a modulation index less than 2.
4.2.1.2. Asynchronous Demodulator
The asynchronous demodulator should be used for OOK modulation and for (G)FSK modulation under one or
more of the following conditions:
Modulation index > 2
Non-standard preamble (not 1010101... pattern)
When the modulation index exceeds 2, the asynchronous demodulator has better sensitivity compared to the
synchronous demodulator. An internal deglitch circuit provides a glitch-free data output and a data clock signal to
simplify the interface to the host. There is no requirement to perform deglitching in the host MCU. The
asynchronous demodulator will typically be utilized for legacy systems and will have many performance benefits
over devices used in legacy designs. Unlike the Si4432/31 solution for non-standard packet structures, there is no
requirement to perform deglitching on the data in the host MCU. Glitch-free data is output from Si446x devices, and
a sample clock for the asynchronous data can also be supplied to the host MCU; so, oversampling or bit clock
recovery is not required by the host MCU. There are multiple detector options in the asynchronous demodulator
block, which will be selected based upon the options entered into the WDS calculator. The asynchronous
demodulator's internal frequency error estimator is able to acquire the frequency error based on any preamble
structure.
4.2.2. RX/TX Data Interface With MCU
There are two different options for transferring the data from the RF device to the host MCU. FIFO mode uses the
SPI interface to transfer the data, while direct mode transfers the data in real time over a GPIO pin.
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